3-Benzyl-2-methylimino-5-phenyl-Δ4 -1,3,4-thiadiazolines and method of combating undesired plant growth

ABSTRACT

A class of 3-benzyl-2-methylimino-5-phenyl-Δ 4  -1,3,4-thiadiazolines which may have certain specific substituents on the benzyl and phenyl rings are useful in combating various weeds in grain crops, for example, grassy weeds in wheat and rice fields.

DESCRIPTION OF THE INVENTION

A class of tautomeric alkyliminothiadiazolines has been disclosed inU.S. Pat. No. 3,522,267 to be useful as herbicides, one compound beingdisclosed to be particularly useful for combating weeds in root crops,such as sugarbeets or onions.

I have discovered that a novel class of nontautomericmethyliminothiadiazolines have distinctly different phytotoxicselectivity and are particularly useful in combating weeds in grains,particularly in wheat and rice fields, being effective at applicationrates of less than 4 lb per acre (4.5 kg. per hectare). The novelherbicidal agents are effective against broadleaf weeds belonging tofamilies of which sugar beets, radishes, tomato, alfalfa and coxcomb arerepresentative species, as well as many pestiferous grasses.

Briefly, my method of combating weeds in grain fields comprises applyingto the area where the combating effect is desired a herbicidallyeffective amount of a compound of the formula: ##STR1## in which R ismethyl or chloro and R' is hydrogen, methyl, trifluoromethyl, benzyloxy,chloro or fluoro, said compound being applied either in unmodified formor in the form of a salt with an acid, in combination with a carrier.Water is a preferred carrier, although other liquid and finely dividedsolid carriers may be used.

Preparation of the Herbicides

The compounds of this invention may be prepared from commerciallyavailable intermediates by means of the procedures which arespecifically exemplified below.

2-Methylamino-5-(3-chlorophenyl)-1,3,4-thiadiazole

A well-stirred mixture of 125 g (0.8 mole) of 3-chlorobenzoic acid and84 g (0.8 mole) of 4-methylthiosemicarbazide in 700 ml of dioxane washeated until the solution was homogeneous. Phosphorus oxychloride (123g, 0.8 mole) was added dropwise to the resulting solution at a rate tomaintain the dioxane at gentle reflux.

After the addition was completed, the mixture was heated at reflux anadditional 45 minutes. The reaction mixture was allowed to cool to roomtemperature and the dioxane was decanted into 1,000 ml of 13 percentaqueous sodium hydroxide solution. The remaining insoluble mass wastransferred to a mortar where it was pulverized. The powdered materialwas added to the aqueous sodium hydroxide-dioxane mixture and the latterwas allowed to stir at room temperature for 150 min. Sufficient waterwas added to the mixture to produce a final volume of 3,500 ml. Thesolution was allowed to stir at room temperature for 75 min. and theinsoluble material was collected on a Buchner funnel. Recrystallizationof the crude product from 95 percent ethanol afforded 108 g of thedesired product. m.p. 141°-43°.

2-Methylimino-3-(4-methylbenzyl)-5-(3-chlorophenyl)-Δ⁴-1,3,4-thiadiazoline

A well-stirred mixture of 150.0 g (0.67 mole) of2-methylamino-5-(3-chlorophenyl)-1,3,4-thiadiazole, 150.0 g (1.07 mole)of a-chloro-p-xylene and 300 ml of dioxane were heated at reflux for 24hr. The reaction mixture was cooled and approximately 400 ml of hexanewas added. The insoluble material was separated by vacuum filtration.The crude salt was added to 600 ml of 10% methanolic potassiumhydroxide. The mixture was allowed to stir at room temperature for 24hr. The resulting solution was diluted to 3,000 ml with water and theinsoluble material was separated by filtration. Recrystallization of thecrude material gave 182 g of the title compound. m.p. 94°-97°.

Preparation of the hydrochloride salt of2-methylimino-3-benzyl-5-(3-chlorophenyl)-Δ⁴ -1,3,4-thiadiazoline

A well stirred mixture of 13.0 g (0.058 mole) of2-methylamino-5-(3-chlorophenyl)-1,3,4-thiadiazole, 13.0 g (0.10 mole)of benzyl chloride and 25 ml of dioxane were heated at reflux for 18 hr.The reaction mixture was cooled, treated with 30 ml of hexane and theinsoluble material collected by vacuum filtration. The crude product wasrecrystallized from a mixture of chloroform-hexane to afford 11.5 g ofthe desired compound. m.p. 96°-98°.

Preparation of the trichloroacetic acid salt of2-methylimino-3-benzyl-5-(3-chlorophenyl)-Δ⁴ -1,3,4-thiadiazoline

To a cold solution of 8.0 g (0.025 mole)2-methylimino-3-benzyl-5-(3-chlorophenyl)-Δ⁴ -1,3,4-thiadiazoline in 25ml of benzene was added a solution of 4.1 g (0.025 mole) oftrichloroacetic acid in 20 ml of benzene. The mixture was allowed tostir at room temperature for 60 minutes and the resulting insolublematerial was separated by filtration, affording 11.0 g of the desiredsalt with a melting point 107°-08°.

Compounds which have been prepared by the above-described procedures arelisted in Table 1.

                  TABLE I                                                         ______________________________________                                        COMPOUNDS OF THE FORMULA                                                       ##STR2##                                                                                                         m.p.C°                             Compound                            or (BP                                    Number  R       R'                  ° C/mm Hg)                         ______________________________________                                        1       chloro  hydrogen            72-73                                     2       chloro  3-methyl            77-78                                     3       chloro  4-methyl            92-94                                     4       methyl  3-chloro            78-80                                     5       methyl  4-methyl            oil at                                                                        room temp.                                6       chloro  3-fluoro            77-79                                     7       chloro  4-fluoro             98-100                                   8       methyl  4-fluoro   (HCl     194-96                                                               salt)                                              9       methyl  4-fluoro            53-54                                     10      methyl  3-trifluoro         193-94                                                    methyl     (HCl                                                                          salt)                                              11      methyl  3-trifluoro-        oil at                                                    methyl              room temp.                                12      chloro  hydrogen   (HCl     196-98                                                               salt)                                              13      chloro  3-trifluoro         206-08                                                    methyl     (HCl                                                                          salt)                                              14      chloro  3-trifluoro-         98-101                                                   methyl                                                        15      chloro  4-methyl   (HCl     193-96                                                               salt)                                              16      chloro  3-fluoro   (HCl     203-05                                                               salt)                                              17      chloro  hydrogen   (CCl.sub.3 CO.sub.2 H                                                                  107-08                                                               salt)                                              18      chloro  4-benzyloxy         121-123                                   19      methyl  4-benzyloxy         91-93                                     ______________________________________                                    

Use of the Herbicides to Combat Weeds

Rice was grown in 4 inch Tufflite (polystyrene foam) pots placed onelectric heating mats. The weed species were grown in 12 inch × 3 inchTufflite flats. Greenhouse potting soil was used in both pots and flats.

Each herbicide was formulated for application by mixing with asolvent-emulsifier mixture to form a water-dispersible concentrate towhich water was then added to form a spray mixture. The solventemulsifier mixture consisted of 60 percent of a commercial emulsifiersold for agricultural use, 20 percent xylene and 20 percent kerosene.

The compounds were applied to various rates, both pre- andpost-emergently to different pots and flats at the same time.Application was made at a spray volume of 40 gal/A with a 6501 nozzle.Herbicides were incorporated in the soil in pre-emergent tests by addingone-fourth inch of soil over the sprayed surface. The tests wereevaluated four weeks after spraying.

The results were scored on the following numerical scale:

0 = no observable injury

1 = temporary injury

2 = some permanent injury

3 = severe injury, some plants died

4 = all plants died

The results are tabulated in Table II.

                                      TABLE II                                    __________________________________________________________________________    EFFECT OF HERBICIDES ON RICE AND WEEDS                                                           green  barnyard                                                                             yellow                                             Appl'n                                                                              Crabgrass                                                                            sprangletop                                                                          grass  foxtail                                                                            smartweed                                                                             rice                            Compound                                                                            Rate  Digitaria                                                                            Leptochloa                                                                           Echinochloa                                                                          Setaria                                                                            Polygonum                                                                             Oryza                           no.   (lb/A)                                                                              sanguinalis                                                                          dubia  crusgalli                                                                            glauca                                                                             pennsylvanicum                                                                        sativa                          __________________________________________________________________________    1     Pre-                                                                          Emergent                                                                      4     4      4      4      4    2       1                                     1     4      4      4      4    1       0                                     1/2   4      4      3      4    1       0                                     1/4   2      1      1      2    0       0                                     Post-                                                                         Emergent                                                                      4     4      4      4      4    4       2                                     1     4      4      4      4    4       0                                     1/2   4      4      4      4    3       0                                     1/4   4      4      4      4    2       0                               2     Pre-                                                                          Emergent                                                                      4     4      4      4      4    1       1                                     1     4      4      3      4    1       0                                     1/2   3      3      2      4    0       0                                     1/4   1      1      1      2    0       0                                     Post-                                                                         Emergent                                                                      4     4      4      4      4    4       1                                     1     4      4      4      4    3       0                                     1/2   4      4      4      4    2       0                                     1/4   4      4      3      4    2       0                               3     Pre-                                                                          Emergent                                                                      4     4      4      4      4    2       2                                     1     4      4      4      4    2       0                                     1/2   4      4      3      4    1       0                                     1/4   3      3      2      3    0       0                                     Post-                                                                         Emergent                                                                      4     4      4      4      4    4       2                                     1     4      4      4      4    4       0                                     1/2   4      4      4      4    3       0                                     1/4   4      4      4      4    2       0                               4     Pre-                                                                          Emergent                                                                      4     4      4      4      4    3       1                                     1     4      4      3      4    1       0                                     1/2   3      4      2      4    1                                             1/4   1      1      0      2    0       0                                     Post-                                                                         Emergent                                                                      4     4      4      4      4    4       1                                     1     4      4      4      4    3       0                                     1/2   4      4      4      4    3       0                                     1/4   4      4      3      4    2       --                              5     Pre-                                                                          Emergent                                                                      4     4      4      4      4    3       1                                     1     4      4      3      4    1       0                                     1/2   2      4      2      3    0       0                                     1/4   1      1      1      2    0       0                                     Post-                                                                         Emergent                                                                      4     4      4      4      4    4       2                                     1     4      4      4      4    3       0                                     1/2   4      4      4      4    3       0                                     1/4   4      4      3      3    2       --                              6     Pre-                                                                          Emergent                                                                      4     4      4      4      4    3       2                                     1     4      4      4      4    1       0                                     1/2   4      4      3      4    1       0                                     1/4   3      4      2      3    0       0                                     Post-                                                                         Emergent                                                                      4     4      4      4      4    4       1                                     1     4      4      4      4    4       1                                     1/2   4      4      4      4    3       0                                     1/4   4      4      4      4    2       0                               7     Pre-                                                                          Emergent                                                                      4     4      4      4      4    2       1                                     1     4      4      4      4    2       0                                     1/2   3      4      3      4    0       0                                     1/4   2      4      2      3    0       0                                     Post-                                                                         Emergent                                                                      4     4      4      4      4    4       1                                     1     4      4      4      4    3       0                                     1/2   4      4      4      4    2       0                                     1/4   4      4      3      3    1       0                               8     Pre-                                                                          Emergent                                                                      2     4             4           1       0                                     1     2             4           0       0                                     1/2   1             2           0       0                                     Post-                                                                         Emergent                                                                      2     4             4           2       2                                     1     2             3           1       0                                     1/2   2             2           0       0                               9     Pre-                                                                          Emergent                                                                      2     4             4           1       0                                     1     3             3           1       0                                     1/2   0             1           0       0                                     Post-                                                                         Emergent                                                                      2     4             4           2       1                                     1     3             3           1       1                                     1/2   1             1           0       0                               10    Pre-                                                                          Emergent                                                                      2     4      4      4           3       1                                     1     4      3      4           1       0                                     1/2   3      2      4           0       0                                     Post-                                                                         Emergent                                                                      2     4             4           4       1                                     1     4             4           3       0                                     1/2   2             4           2       0                               11    Pre-                                                                          Emergent                                                                      2     4      4      4           3       1                                     1     4      4      4           2       0                                     1/2   4      3      4           2       0                                     Post-                                                                         Emergent                                                                      2     4             4           4       2                                     1     4             4           3       0                                     1/2   3             4           2       0                               12    Pre-                                                                          Emergent                                                                      2     3      3      4           1       0                                     1     1      3      2           0       0                                     1/2   1      1      1           0       0                                     Post-                                                                         Emergent                                                                      2     3             4           1       1                                     1     2             4           2       0                                     1/2   3             4           1       0                               13    Pre-                                                                          Emergent                                                                      2     4      4      4           1       0                                     1     3      4      3           0       0                                     1/2   2      4      2           0       0                                     Post-                                                                         Emergent                                                                      2     3             4           2       0                                     1     2             3           2       0                                     1/2   1             3           0       0                               14    Pre-                                                                          Emergent                                                                      2     4      4      4           1       0                                     1     4      4      3           0       0                                     1/2   1      3      2           0       0                                     Post-                                                                         Emergent                                                                      2     3             4           3       1                                     1     2             4           1       0                                     1/2   1             3           0       0                               15    Pre-                                                                          Emergent                                                                      2     4             4           2       1                                     1     3             3           3       0                                     1/2   1             2           0       0                                     Post-                                                                         Emergent                                                                      2     3             4           3       1                                     1     1             1           0       0                                     1/2   1             0           0       0                               17    Pre-                                                                          Emergent                                                                      2     4      4      4           3       1                                     1     4      4      4           2       0                                     1/2   1      3      4           0       0                                     Post-                                                                         Emergent                                                                      2     4             4           4       1                                     1     4             4           2       1                                     1/2   2             4           1       0                               __________________________________________________________________________

The herbicides of this invention do not present unique formulationproblems and may be readily formulated by conventional techniques,employing solvents, diluents, solid carriers and surface active agentswhich are commercially available and are approved for agricultural use.The herbicides of this invention are all nitrogen bases which readilyform salts with strong acids and in fact are most conveniently preparedas hydrohalide salts. They may be formulated and applied in salt form ifit is more convenient to do so. However, by converting the salt form tothe free base as illustrated in procedures disclosed above, a product isobtained which is soluble in a greater variety of organic solvents. Thismay be considered more desirable from the standpoint of formulationeconomy. It should be kept in mind that the salt form has a greaterweight, mole for mole, than the free base and this must be taken intoaccount in formulating to a desired concentration of active agent.

Some of the compounds listed in Table I have outstanding utility ofcertain specific types. Compounds numbered 1, 9, 12 and 16 may be usedto particular advantage in combination with the commercial herbicidebarban to give broad spectrum weed control in wheat. Compounds numbered18 and 19 are broadly useful in combating weeds in a number of smallgrain crops, including wheat, oats and rice. The latter two compoundsare readily prepared by the reaction of the commercially available4-benzyloxybenzyl chloride with either2-methylamino-5-(3-methylphenyl)-1,3,4-thiadiazole or2-methylamine-5-(3-chlorophenyl)-1,3,4-thiadiazole by proceduresdescribed above. The reaction is conveniently carried out in refluxingdioxane as a reaction solvent, followed by neutralization of theresulting mixture with methanolic sodium hydroxide and recovery of theproduct as in the procedure exemplified above for the corresponding4-methylbenzyl compound. The compounds mentioned above which havespecific utility for weed control in wheat were evaluated in thegreenhouse in comparative tests on wheat and five associated weedspecies by the procedure described above and results were ratedaccording to the same schedule employed in Table II. The results appearbelow in Tables III and IV. In areas in which sugar beets, rape andsmall grains are grown, a small group of particularly troublesome weedsand volunteer crop plants often fluorish in competition with the cropsand each other. Compounds 18 and 19 were used pre-emergently accordingto above-described procedures on sugar beets, rape and a small number ofassociated weeds. Results appear in Table V.

                                      TABLE III                                   __________________________________________________________________________    EFFECT OF HERBICIDES ON WHEAT AND ASSOCIATED WEEDS                                                     Wild   Wild   Green                                                                              Wild     Downy                                     Pigweed Buckwheat                                                                            Mustard                                                                              Foxtail                                                                            Oats                                                                              Wheat                                                                              Brome                    Compound  Application                                                                          Amaranthus                                                                            Polygonum                                                                            Brassica                                                                             Setaria                                                                            Avena                                                                             Triticum                                                                           Bromus                   no.       Rate (lb/A)                                                                          retroflexus                                                                           convolvulus                                                                          kaber  viridis                                                                            fatus                                                                             aestivum                                                                           tectorum                 __________________________________________________________________________     1    PRE 4      4              3      4    2   1    2                                  2      4              1      4    1   0    1                                  1      4              1      4    1   0    0                                  1/2    2              0      3    0   0    0                              POST                                                                              4      4       4      4      4    3   1                                       2      4       4      4      4    1   0                                       1      4       4      4      3    1   0                                       1/2    4       1      4      1    0   0                              9    PRE 4      4              2      4    3   1    3                                  2      4              2      4    1   1    2                                  1      4              1      4    0   0    1                                  1/2    4              0      4    0   0    0                              POST                                                                              4      4       4      4      4    3   1                                       2      4       4      4      4    1   0                                       1      4       4      4      3    1   0                                       1/2    4       4      4      2    1   0                             12    PRE 4      4              3      4    2   1    1                                  2      4              1      4    1   0    1                                  1      3              1      4    0   0    1                                  1/2    1              0      2    0   0    0                              POST                                                                              4      4       4      4      4    3   1                                       2      4       4      4      4    2   0                                       1      4       3      4      2    1   9                                       1/2    4       3      4      2    0   0                             16    POST                                                                              4      4       4      4      4    3   1                                       2      4       4      4      4    2   0                                       1      4       4      4      3    2   0                                       1/2    3       3      4      2    1   0                             barban                                                                              POST                                                                              1/2    0              0      0    4   0    1                                  1/4    0              0      0    4        0                        __________________________________________________________________________

                                      TABLE IV                                    __________________________________________________________________________    POST-EMERGENT EFFECTS OF COMBINATIONS OF HERBICIDES WITH                      BARBAN ON WHEAT AND ASSOCIATED WEEDS                                                                        Downy                                                                              Wild Green                                                                              Wild                                                   Pigweed Brome                                                                              Mustard                                                                            Foxtail                                                                            Oats                                                                              Wheat                        Compound                                                                            Application                                                                           Barban  Amaranthus                                                                            Bromus                                                                             Brassica                                                                           Setaria                                                                            Avena                                                                             Triticum                     no.   Rate (lb/A)                                                                           Rate (lb/A)                                                                           retroflexus                                                                           tectorum                                                                           kaber                                                                              viridis                                                                            fatua                                                                             aestivum                     __________________________________________________________________________    1     2       1/4     4       4    4    4    4   2                                  1       1/4     4       4    4    4    4   1                                  1/2     1/4     4       3    4    4    4   1                            9     2       1/4     4       4    4    4    4   2                                  1       1/4     4       4    4    4    4   2                                  1/2     1/4     4       3    4    4    4   1                            12    2       1/4     4       4    4    4    4   1                                  1       1/4     4       3    4    4    4   2                                  1/2     1/4     4       2    4    4    4   1                            16    2       1/4     4       3    4    4    4   1                                  1       1/4     4       3    4    4    4   0                                  1/2     1/4     4       2    4    4    4   0                            __________________________________________________________________________

                                      TABLE V                                     __________________________________________________________________________    PRE-EMERGENCE USE OF HERBICIDES AGAINST                                       SUGAR BEETS, RAPE AND ASSOCIATED WEEDS                                                           Lambs-        Sugar     Wild                                                                              Green                                        Kochia                                                                             quarters                                                                             Pigweed                                                                              Beets                                                                              Rapeseed                                                                           Oats                                                                              Foxtail                        Compound                                                                            Application                                                                           Kochia                                                                             Chenopodium                                                                          Amaranthus                                                                           Beta Brassica                                                                           Avena                                                                             Setaria                        no.   Rate (lg/A)                                                                           scoparia                                                                           album  retroflexus                                                                          vulgaris                                                                           napus                                                                              fatua                                                                             viridis                        __________________________________________________________________________    18    4       4    2      4      4    4    2   4                                    2       3    2      4      4    4    1   4                                    1       3    2      4      3    4    1   4                                    1/2     2    0      4      2    3    0   3                              19    4       3    4      4      4    4    1   4                                    2       3    4      4      4    4    0   4                                    1       3    4      4      3    3    0   4                                    1/2     2    2      4      1    1    0   3                              __________________________________________________________________________

I claim:
 1. The method of combating weeds in grain fields whichcomprises applying to the area where the combating effect is desired aherbicidally effective amount of a compound of the formula ##STR3## inwhich R is methyl or chloro and R' is hydrogen, methyl, trifluoromethyl,chloro or fluoro, said compound being applied either in unmodified formor in the form of a salt with an acid in combination with an inertcarrier.
 2. The method according to claim 1 which comprises applying tothe area where the combating effect is desired a herbicidally effectiveamount of 3-benzyl-5-(3-chlorophenyl)-2-methylimino-Δ⁴-1,3,4-thiadiazoline in combination with an inert carrier.
 3. The methodaccording to claim 1 which comprises applying to the area where thecombating effect is desired a herbicidally effective amount of5-(3-chlorophenyl)-3-(3-methylbenzyl)-2-methylimino-Δ⁴-1,3,4-thiadiazoline in combination with an inert carrier.
 4. The methodaccording to claim 1 which comprises applying to the area where thecombating effect is desired a herbicidally effective amount of5-(3-chlorophenyl)-3-(4-methylbenzyl)-2-methylimino-Δ⁴-1,3,4-thiadiazoline in combination with an inert carrier.
 5. The methodaccording to claim 1 which comprises applying to the area where thecombating effect is desired a herbicidally effective amount of3-(3-chlorobenzyl)-2-methylimino-5-(m-tolyl)-Δ⁴ -1,3,4-thiadiazoline incombination with an inert carrier.
 6. The method according to claim 1which comprises applying to the area where the combating effect isdesired a herbicidally effective amount of3-(4-methylbenzyl)-2-methylimino-5-(m-tolyl)-Δ⁴ -1,3,4-thiadiazoline incombination with an inert carrier.
 7. The method according to claim 1which comprises applying to the area where the combating effect isdesired a herbicidally effective amount of5-(3-chlorophenyl)-3-(3-fluorobenzyl)-2-methylimino-Δ⁴-1,3,4-thiadiazoline in combination with an inert carrier.
 8. The methodaccording to claim 1 which comprises applying to the area where thecombating effect is desired a herbicidally effective amount of5-(3-chlorophenyl)-3-(4-fluorobenzyl)-2-methylimino-Δ⁴-1,3,4-thiadiazoline in combination with an inert carrier.
 9. The methodaccording to claim 1 which comprises applying to the area where thecombating effect is desired a herbicidally effective amount of3-(4-fluorobenzyl)-2-methylimino-5-(m-tolyl)-Δ⁴ -1,3,4-thiadiazoline incombination with an inert carrier.
 10. The method according to claim 1which comprises applying to the area where the combating effect isdesired a herbicidally effective amount of2-methylimino-5-(m-tolyl)-3-(3-trifluoromethyl)-benzyl-Δ⁴-1,3,4-thiadiazoline in combination with an inert carrier.
 11. Themethod according to claim 1 which comprises applying to the area wherethe combating effect is desired a herbicidally effective amount of5-(3-chlorophenyl)-2-methylimino-3-(3-trifluoromethylbenzyl)-Δ⁴-1,3,4-thiadiazoline in combination with an inert carrier.